Differential Code Biases (DCBs) are the systematic errors, or biases, between two GNSS code observations at the same or different frequencies. DCBs are required for code-based positioning of GNSS receivers, extracting ionosphere total electron content (TEC), and other applications. Proper knowledge of DCBs is crucial to many navigation applications but also non-navigation applications such as ionospheric analysis and time transfer. With all of the new signals offered by modernized and new GNSS constellations, analysts now require a comprehensive multi-GNSS DCB product.

As part of the IGS Multi-GNSS Experiment (MGEX) two different DCB products are determined by two analysis groups: Institute of Geodesy and Geophysics (IGG) of the Chinese Academy of Sciences (CAS) in Wuhan and the Deutsche Forschungsanstalt für Luftund Raumfahrt (DLR) in Germany. These files are archived at the CDDIS:

https://cddis.nasa.gov/archive/gnss/products/bias/

The satellite and station biases computed by the Institute of Geodesy and Geophysics (IGG) of the Chinese Academy of Sciences (CAS) in Wuhan are generated on a daily basis with a latency of 2-3 days and made available in daily BSX files. The constellations and signals analyzed by the IGG CAS are:

Constellation	Analyzed Signals
GPS	C1C,C1W,C2L/S/X,C2W,C5Q/X
GLO	C1C,C1P,C2C,C2P
GAL	C1C/X,C5Q/X,C7Q/X,C8Q/X
BDS	C2I,C6I,C7I

Reference: Wang N., Yuan Y., Li Z., Montenbruck O., Tan B. (2016) Determination of differential code biases with multi-GNSS observations, Journal of Geodesy, Vol. 90, No. 3, pp. 209-228, DOI 10.1007/s00190-015-0867-4

The DLR product is updated on a 3-monthly basis and comprises weekly averages of the satellite biases. In addition a full set of daily satellite and station biases is provided for reference purposes and trend analyses. The constellations and signals analyzed by the DLR are:

Constellation	Analyzed Signals
GPS	C1C,C1W,C2L/S/X,C2W,C5Q/X
GLO	C1C,C1P,C2C,C2P
GAL	C1C/X,C5Q/X,C7Q/X,C8Q/X), in addition GAL(C6C) since Q2/2017
BDS	C2I,C6I,C7I

Reference: Montenbruck O., Hauschild A., Steigenberger P. (2014), Differential Code Bias Estimation using Multi-GNSS Observations and Global Ionosphere Maps, Navigation - Journal of the ION, Vol. 61, No. 3, pp. 191-201, DOI 10.1002/navi.64

Data Format

The CAS DCBs are provided in a preliminary version of the Bias SINEX (BSX) format whereas DLR used the Version 1.00 of February 2016 until Q4/2016 and the Version 1.00 of December 2016 starting with Q1/2017. The December 2016 version of the Bias SINEX format uses a 4-digit year number whereas the version of February 2016 uses a 2-digit year number for specifying the validity intervals.

Bias SINEX 0.01
http://www.biasws2012.unibe.ch/docs/sinex_bias_0.01-2.txt

Bias SINEX 1.00 (February 2016)
http://www.aiub.unibe.ch/download/bcwg/format/draft/sinex_bias_100_feb07.pdf

Bias SINEX 1.00 (December 2016)
http://www.aiub.unibe.ch/download/bcwg/format/draft/sinex_bias_100_dec07.pdf

File Naming

The DCB file names

CAS0MGXRAP_YYYYDDD0000_01D_01D_DCB.BSX.gz
DLR0MGXFIN_YYYY0010000_NNU_07D_DCB.BSX.gz
DLR0MGXFIN_YYYY0010000_NNU_01D_DCB.BSX.gz

are based on a new naming scheme proposed for future MGEX products, which is inherited from the new RINEX3 file naming convention; the full specification is given as

AAAVPPPTTT_YYYYDDDHHMM_LEN_SMP_CNT.FMT[.?*]

where:

Position in Filename	Code	Meaning
01-03	AAA	3-char AC name; here: CAS = Chinese Academy of Sciences DLR = German Aerospace Center
04	V	1-char version/solution identifier; here: nominally 0
05-07	PPP	3-char campaign/project specification; here: MGX
08-10	TTT	3-char product type specification; here: RAP = rapid FIN = final
11	_	1-char separator (underline)
12-15	YYYY	4-digit year of start epoch
16-18	DDD	3-digit day-of-year of start epoch
19-20	HH	2-digit hour of start epoch; here: 00
21-22	MM	2-digit minute of start epoch; here: 00
23	_	1-char separator (underline)
24-26	LEN	2-digits+1-char intended (nominal) product period; here: 01D for 1-day 01Y for 1-year ??L for coverage interval in months
27	_	1-char separator (underline)
28-30	SMP	2-digits+1-char sampling interval; here: 01D = 1-day averages 07D = 7-day averages
31	_	1-char separator (underline)
32-34	CNT	3-char content type; here: DCB
35	.	1-char separator (dot)
36-38	FMT	3-char format extension; here: BSX
39 (optional)	.	1-char separator (dot)
40-xx (optional)	extension	compression file type; here: gz